This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
In general, control signaling information carried on PUCCH (also referred to as Uplink Control Information (UCI)) includes:                Scheduling Requests (SRs);        dynamic HARQ feedback (ACK/NACK) in response to downlink data packets on Physical Downlink Shared CHannel (PDSCH); and        Channel Quality Indicator (CQI), which for the purposes of control signaling categorization.        
In the Long-Term Evolution (LTE) system, the PUCCH supports seven different formats depending on UCI to be signaled. The mapping between PUCCH formats and corresponding UCI supported in LTE is shown in the following Table 1.
TABLE 1Supported uplink control information formats on PUCCHPUCCHFormatUCIFormat 1SR (un-modulated waveform)Format 1a1-bit HARQ ACK/NACK with/without SRFormat 1b2-bit HARQ ACK/NACK with/without SRFormat 2CQI (20 coded bits)Format 2CQI and 1- or 2-bit HARQ ACK/NACK (20 bits) forextended CP onlyFormat 2aCQI and 1-bit HARQ ACK/NACK (20 + 1 coded bits)Format 2bCQI and 2-bit HARQ ACK/NACK (20 + 2 coded bits)
Some Physical Resource Blocks (PRBs) in UpLink (UL) are reserved as PUCCH for CQI, SR and dynamic HARQ ACK/NACK feedback. Resources for the dynamic HARQ feedback are Control Channel Element (CCE)-mapped according to the maximum number of CCEs and the ACK/NACK bundling window size with assumption that every CCE is assigned to a different user which needs a corresponding HARQ feedback resource. For example, a resource index for the dynamic HARQ ACK/NACK feedback is implicitly determined based on the index of the first Control Channel Element (CCE) of the downlink control assignment as:nPUCCH(1)=(M−m−1)×Np+m×Np+1+nCCE+NPUCCH(1)  (1)where nCCE is the number of the first CCE used for transmission of the corresponding PDCCH in subframe n−km, where km is the smallest value in set K such that UE detects a PDCCH in subframe n−km (see, e.g., 3GPP TS 36.213 V10.4.0).
In view of this, resources for the UE transmitting the dynamic HARQ feedback in PUCCH format 1a/1b may be referred to as CCE-mapped dynamic HARQ feedback resources. However, in the real systems, the number of scheduled users is limited and CCE aggregation level is not always equal to 1. That means that the CCE-mapped dynamic HARQ feedback resources might be over-reserved, thereby resulting in ineffectiveness.
With introduction of carrier aggregation in the LTE-advanced (LTE-A) system, a PUCCH format 1b with channel selection is defined in Release 10 for supporting carrier aggregation (see 3GPP TS 36.213 V10.4.0). A UE that supports carrier aggregation at most 2 serving cells shall use PUCCH format 1b with channel selection for transmission of HARQ-ACK (HARQ feedback including ACK/NACK). The PUCCH format 1b with channel selection requires more PUCCH format 1b resources. To be specific, in carrier aggregation with 2 serving cells, the PUCCH format 1b with channel selection is adopted for DownLink (DL) HARQ feedback. In each UL PUCCH transmission, one of 4 PUCCH format 1 b resources (channels) is selected to transmit HARQ feedback. Thus, 4 (channels)×2 (format 1 b bits)=16 feedback states (4 HARQ bits) can be reported in each UL PUCCH transmission. Usually, the first two PUCCH format 1b resources are determined according to nCCE and nCCE+1 mapped dynamic HARQ feedback resources. The last two PUCCH format 1b resources are assigned dynamically in each DL assignment by selecting one of 4 pre-configured channel selection resource sets. Each channel selection resource sets contains two PUCCH format 1b resources.
Usually, PUCCH resources reserved for SR are used for the PUCCH format 1b with channel selection, as illustrated in FIG. 1. As shown, the PUCCH format 1b with channel selection resources are non-overlapped with dynamic HARQ feedback resources. With a given number of PUCCH format 1/1a/1b PRBs, the total number of PRBs for SR is decreased (e.g., 8 SR users per UL subframe is occupied), thereby resulting in significant degradation of system capacity due to SR reduction. Alternatively, more PUCCH PRBs need to be reserved to guarantee the SR capacity, which results in UL throughput degradation.